Various channel estimation methods are used in different cellular communications systems. One cellular network system, referred to as the third generation partnership project (3GPP) work item on the Long Term Evolution (LTE), is widely used for wireless communications. In the current 3GPP LTE downlink standard, channel estimation at user equipment (UE) is performed per physical resource block (PRB) or per PRB group (PRG), when user-specific demodulation reference signal (DM-RS) symbols are utilized. From the channel state information (CSI) feedback perspective, two operation modes of feedback are possible: wideband and frequency selective precoding matrix indicator (PMI) and channel quality indicator (CQI) feedback.
Unlike transmission schemes using cell-specific reference symbols (CRS), transmission schemes using spatially precoded user-specific reference symbols DM-RS do not require precoding matrix knowledge at the receiver for data demodulation, because precoding matrix is included implicitly in the channel estimation. In general, reliable channel estimation is needed at the demodulation stage. It has been shown, for example, during the work on the topic of the network aided interference cancellation and suppression (NAICS) in LTE release 12, not only the desired stream channel estimation is important, but also equally reliable channel estimation needs to be performed so that the dominant interference can be cancelled or eliminated at the UE side by means of non-linear advanced receivers. Moreover, for the interfering UE, a blind detection stage of modulation is needed in addition to the channel estimation in order to allow the applicability of non-linear receivers such as symbol level interference cancellation (SLIC) receivers. As the blind detection of the modulation is performed based on the effective channel of the interferer, it is evident that reliability of such channel estimation is crucial.
It is well noted that the quality of channel estimation has an impact on data demodulation performance of the receiver. Thus, improving the channel estimation at a receiver is always desirable regardless whether the receiver has interference cancellation capability.